Structures that can be deployed in space, for example of the solar generator type, are generally made up of rigid panels articulated together, these panels, when in the stored position, being stacked on top of one another. These structures have the advantage of kinematics that are well controlled but have the disadvantage of high specific mass and high inertia. Further, when in the stored position, the rigid structures occupy a significant amount of space under the fairing of a launcher. Because the space under the fairing of a launcher allocated to the deployable structures is limited, it is important to reduce the amount of space required by these deployable structures when they are in the stored position in order to optimize the area they can occupy when deployed.
There are deployable flexible planar structures that comprise a flexible sheeting and tape springs which are fixed to one and the same plane of the sheeting. In the stored position, the sheeting and the tape springs are wound around a mandrill. The flexible planar structure is deployed autonomously by the spontaneous unwinding of the tape springs when the mandrill is free to rotate.
Indeed, tape springs are known in the field of space as being flexible tapes with a cross section in the form of a circular arc, the radius of curvature of which is convex on a first face and concave on a second face, these tapes being able to pass from the wound state to the unwound state essentially as a result of their own stored elastic energy. There are different types of tape each of which has its own properties. Monostable tapes have a deployed natural position and need retention to keep them in a stored position. Monostable tape springs therefore have a natural tendency to deploy in order to revert to their unwound state. The deployment of monostable tapes is often haphazard and uncontrolled. Bistable tapes have two natural positions (stored position and deployed position) and do not require retention to keep them in the stored position when the cross section is completely flattened. Their deployment is linear and controlled. However, in all cases, when deployment is triggered deployment may be violent and jerky, which means to say that the entire tape spring may have a tendency to straighten out all at once, over the entire length, presenting a risk of damaging surrounding elements or elements fixed to the tape spring such as a flexible membrane, an instrument, an antenna, etc. Conventional tape springs may thus exhibit difficulties in terms of control over their deployment. In order to regulate the speed at which this type of structure deploys, there are a number of methods that can be used. Mention may for example be made of regulation using a geared electric motor unit as described in patent application FR12/03300 or thermal regulation using hybrid tape springs as described in patents FR 0803986 and U.S. Pat. No. 7,856,735.
Furthermore, tape springs do not have the same stiffness depending on the axis of strain. A force F applied to the convex face of the tape spring will have a tendency to cause the tape spring to flex whereas the same force applied to the concave face will have no effect, thereby presenting a problem of instability of the flexible structure in its deployed state. In order to address this problem of stability in the deployed state, it is therefore necessary to keep the tape spring in the deployed position using an additional retaining device or to over-engineer the tape spring in order to ensure that it remains stable under the forces of orbiting, whatever the direction in which these are applied.
Thus, in the stored configuration, the tape spring needs to be as compact as possible, namely to have the smallest possible radius of winding. This parameter is set by the physical characteristics of the tape; generally, the radius of winding is substantially equal to the radius of curvature of the tape. In the case of a composite tape, this can be altered by changing the layering of the plies and/or the direction of the fibres. In the deployed configuration, the best possible rigidity is sought, which means the largest and most closed cross section possible, associated with the end of the tape spring being encastré as extensively as possible. In general, tape spring deployment is obtained by the unwinding of the tape spring around a mandrill. During deployment, the tape spring has a rigidity which is downgraded on account of the natural flexibility of the tape spring in the zone of winding thereof. Optimum rigidity is obtained at the end of deployment when the unwinding zone is replaced by a true encastré status. Nevertheless, it is sometimes desirable for the deployable structure to be operational throughout the tape spring deployment phases, namely in a configuration of total or of partial deployment. In the case of a rewindable deployable structure, it is necessary to have the anchorage of the tape spring encastré so as to guarantee rigidity consistent with the requirement. In order to achieve this, use is generally made of a guide ramp equipped with rollers making it possible simultaneously to achieve extraction of the tape spring and adequate encastré status. This solution is compatible with the requirement but presents various problems, namely a risk of unwanted bracing or unwinding of the tape spring if the stored energy of the tape spring is to be used, haphazard kinematics of the end of the tape and a significant volume often incompatible with the volume allocated for storage.
Because the diameter of the tape spring changes throughout deployment, it is necessary to afford numerous additional guides, at the exit of the tape spring, in order to ensure that the deployable structure as a whole functions correctly.